It is known to send both voice and data over various types of communications channels. Several methods are known for sending data over the control channels of a wireless telecommunications network. One example is the standard IS-41 signaling over the control channel. Other known messaging services include SMS or Short Message Service which allows up to 160 characters to be sent over the air from base stations to cell phones, pagers or other handheld wireless devices, again operating separately from the voice channel. WAP or Wireless Application Protocol is a carrier-independent, transaction oriented protocol for wireless data networks. It is currently being implemented in various wireless devices to enable interactive sessions using “mini-web pages” or the like. One cannot simultaneously carry on a conversation over the same channel. Thus a WAP session is not a voice channel connection.
Others have attempted to insert data in the form of audio tones—similar to a conventional telephone modem—into the voice channel of a wireless session. One problem is that such tones are audible, and therefore they interfere with the voice conversation. One known solution to that interference calls for essentially turning off the voice connection, e.g., the microphone and speaker, at predetermined intervals, and transmitting data over the voice channel during that brief interval. This approach is aptly called “blank and burst.” Up to a few hundred milliseconds of “blank and burst” at a time may go unnoticed by the caller, but the amount of data that can be transferred over that interval is quite limited, due to the limited frequency response and corresponding bandwidth of the channel.
Another approach is to carve a “notch” in the voice channel frequency spectrum, and modulate the data for insertion into the notch of frequencies no longer occupied by voice content. Of course, voice fidelity is compromised, and again bandwidth of data transmission is severely limited. This notch filter technology was described by Bruno, et al., in PCT Publication No. WO 96/18275 which corresponds to U.S. Pat. No. 6,226,529. It also appears in U.S. Pat. No. 6,140,956 to Hillman, et al. Both of these U.S. patents are incorporated herein by this reference.